1. Field of the Invention
The present disclosure relates to wireless roaming, and more particularly to a system and method for vertical handoff in a wireless network.
2. Discussion of Related Art
Wireless connectivity is a burgeoning market in which consumers are coming to expect network access in a variety of venues, such as malls, hotels, public spaces, etc. Wireless Local Area Networks (WLAN) are providing the connectivity.
Within these venues dead zones are a problem. Dead zones are pockets within a WLAN having reduced or no wireless signal for connecting to the network. As a mobile node moves into a dead zone, any connection to the network will be substantially degraded or dropped. The dead zones detract from the users experience of wireless connectivity.
One method of limiting dead zones is to implement a network comprising different wireless technologies having different capabilities in a given geographic area. For a wireless device to move within such a network, a handoff is needed between wireless network cells to provide continuous connections to the network.
Handoffs in wireless mobile networks can be characterized into two categories, horizontal handoff and vertical handoff. Horizontal handoff allows mobile nodes to move among wireless network cells that support the same wireless link technology. Vertical handoff allows device movement within a network environment that comprises heterogeneous wireless links.
Because vertical handoff involves different types of connections, e.g., 802.11 and General Packet Radio Service (GPRS), handing a connection from one cell to another is slow as compared to horizontal handoff, and detracts from a user's wireless experience. For example, until the new connection is established, the mobile node is cut off from the network. Further, packet loss or delay during a handoff interval can incorrectly trigger a congestion control mechanism at the sender side of any Transmission Control Protocol (TCP) connections in which the mobile node is involved, thus greatly slowing down the throughput.
No known system or method exists for seamless vertical handoff between different wireless technologies. Therefore, a need exists for a system and method for performing a seamless vertical handoff.